The mobile telephone industry has been associated with tremendous growth over the last several years. For instance, in the recent past, mobile telephones were only available to those of highest economic status due to service costs and costs associated with mobile phones. In contrast, today's portable phones (and other portable devices) have become relatively inexpensive and more widely utilized by large numbers of consumers. Furthermore, many mobile network service providers offer phones at extremely low cost to customers who contract for service with such providers. Contracts of this nature typically involve a small monthly service fee and allow a consumer to pay for the phone and the service in small increments over time. The flexible methods for purchasing mobile phones and mobile phone services have opened up these devices to members of all economic status.
In conjunction with their increased popularity, mobile phones have rapidly developed increased computing capabilities. More specifically, commonly available mobile phones can be utilized as full-service computing machines. For example, many of the most recent and advanced mobile phones can be associated with word processing software, accounting software, and various other types of software. Furthermore, network coverage has expanded to cover millions, if not billions, of users. Additionally, mobile phones have decreased in size. Specifically, modern mobile phones are often small enough to slip into an individual's pocket without discomforting the individual.
Advances in technology relating to mobile devices in general, and mobile phones in particular, continue to occur. For example, recently mobile telephones have been designed to communicate over disparate networks and/or between licensed and unlicensed spectra. In more detail, a multimode handset can connect to a cellular network to effectuate communications between a user of the mobile phone and another phone device, and can further connect by way of WiFi, Bluetooth, and the like and thereafter utilize the Voice over Internet Protocol (VoIP) (or other suitable protocol) to effectuate communication between users. Use of VoIP is often desirable to users as it is associated with less cost than employing a cellular network. In fact, some users may consider phone calls made over VoIP (or other IP-based network) completely free, despite the fact that they pay for Internet service.
Implementation of this multimode service is due at least in part to the Third Generation Partnership Project (3GPP) and Third Generation Partnership Project 2 (3GPP2), and similar standardization efforts, which have created specifications that define a mechanism that provides signal integrity for session initiation protocol (SIP) signals between an IP multimedia subsystem (IMS) and user equipment (UE) (e.g., a mobile phone, a personal digital assistant, . . . ). This integrity prevents identity spoofing, man-in-the-middle attacks, and the like. The IMS represents a 3GPP and 3GPP2 effort to define an all-IP-based wireless network as a replacement for the various voice, data, signaling, and control network elements currently in existence. Furthermore, the IMS enables support for IP multimedia applications within the Universal Mobile Telecommunications System (UMTS). The UMTS includes a 3G broadband packet-based transmission of text, digitized voice, video, and multimedia that offers a consistent set of services to mobile computer and phone users regardless of their physical location.
The telecom industry is currently shifting towards all IP-systems, thereby rendering multimode service handsets an important tool (as they are compatible with existing cellular systems and emerging IP-systems). This shift is driven by desires to reduce costs and create new streams of revenue while protecting an operator business model. IMS is a new service domain that facilitates this shift by enabling convergence of data, speech, and network technology over an IP-based infrastructure. For users, IMS-based services enable transmittal and receipt of various data at significantly reduced cost, including voice, text, pictures, video, and/or any combination thereof in a highly personalized and secure manner. In summary, IMS is designed to bridge the gap between existing, traditional telecommunications technology and Internet technology that increased bandwidth does not provide.
As stated above, these emerging IP-based technologies have created demand for multimode services, and thus for multimode handsets. Using this technology, users can employ one of the many wireless LAN (WLAN) and cellular technologies supported by the handset to effectuate voice calls, transmission of data, and the like. WLAN networks are traditionally based upon an IP infrastructure and therefore inherently support IP based communication. Telecommunication networks have had to alter infrastructure components and protocols in order to integrate IMS-based IP data services, however. This work is currently under way, as traditional second generation (2G) circuit-switched voice transmission infrastructure and protocols are overlaid or replaced with third generation (3G) IMS and IP telecommunication counterparts.
At present, mobile phones often encounter both 2G and 3G networks while maintaining radio frequency (RF) contact with a telecom provider since the full transition from 2G to 3G networks will take some years to complete. Because, in general, a fully functional 3G network is required to provide IMS services, availability of those services can dissipate when a mobile phone switches, or is handed-off, from a 3G to a 2G network. Handoff commonly occurs when a mobile phone roams a distance away from a RF network component greater than that required to maintain strong RF contact. Contact with another component must be established instead, so the mobile phone is handed-off from one component to another. Compounding this problem is the fact that a geographical area covered by a network can fluctuate over time depending on several factors, including signal interference with neighboring networks and an amount of RF traffic being handled at a given time. This implies that a mobile phone may be handed off from a 3G to a 2G network even while remaining stationary, resulting in a loss of 3G services. Moreover, due to restrictions in VoIP emergency call services, if a mobile phone is handed-off from a 3G to a 2G network during a call, it must remain on the 2G network until the call is completed. If a mobile subscriber had been in the midst of utilizing a 3G service transmission during that call, for example streaming real-time video simultaneously with the telephone call, an abrupt loss of services can be frustrating. Furthermore, the VoIP restrictions require the mobile user to end the call before reacquiring a 3G network signal and resuming a video share application.
Until the 3G network infrastructure is complete and mature, it can be difficult to prevent interruption of services flowing from a 3G to 2G handoff. Worse still, when handoff occurs frequently, a dubious light can be cast upon otherwise robust services. It is of utmost import that a mobile provider's services appear robust at a user-level, however, or the reputation and acceptance of those services can falter.